Telephone system



TELEPHONE SYSTEM Filed Oct. 10, 1929 '--InTn"ZFfi---- William Georg-2 521mm Patented Dec. 6, 1932 UNITED STATES, PATENT OFFICE WILLIAMGEORGE PATTERSON, or LoNnoN, ENGLAND, AssIGNoR T SIEMENS BROTHERS & COMPANY LIMITED, on LONDON, ENGLA D TELEPHONE SYSTEM Application filed October 10, 1929, Serial No. 398,607, and in Great Britain October 1'7, 1928.

' The present invention relates to telephone systems.

In some telephone systems it is usual to transmit a supervisory signal by reversing the polarity of the line wires. For instance, when the called subscriber replies, the polarity of the wires forming a part of the speaking circuit is reversed to effect the operation of the calling subscribers meter. This reversal causes objectionable clicks in the subscribers receiver and the present invention has in view the reduction in intensity of these clicks.

The reversal of polarity of the line wires usually takes place at a feeding bridge where current is fed to the line over retard coils or windings of a relay or relays, the reversal being efiected by contacts of a supervisory relay which contacts are in direct connection with the line. 7 V I In the present invention impedance is included in the feeding bridge between the line and the reversing contacts. The impedance may be the windings of a relay, for instance, the impulse relay of a selector in an automatic telephone system. When reversal takes place, the eifect of the impedanceprovided is to decrease the rate at which current in the line changes, thus reducing the intensity of the clicks referred to.

To reduce still further the objectionable click a condenser may be connected to the two ends of the impedance coils remote from the line. The reversing contacts may be of the ordinary change-over type or contacts of the make-before-break type may be employed in conjunction with a safety guard resistance in the battery connections.

In an automatic telephone system it would be preferable to arrange that the guarding resistance is not in the impulse circuit, but is first brought in when the contacts are in the make-before-break condition.

If the feeding bridge is arranged for the transmission "of equal potential lamp flash signal by disabling one of the contacts of they supervisory relay as described in British Specification No. 271,142, the contact which brings about such disablement would be included between the impedance and the battery connection.

The accompanying drawing shows by way of example a feeding bridge of atype commonly employed at automatic selecting switches and repeaters in an automatic telephone system. Fig. 1 shows an arrangement where reversal of current only is effected at the bridge. In Fig. 2 provision is made-for the transmission of an equipotential lamp flash signal. Y

Referring to Fig. 1, the incoming and out 7 going speaking wires are separated as regards continuous current by the condensers C. To

the outgoing wires on the right of the condensers current is fed from theexchange battery over windings of the answering supervisory relay D. To the incoming wires on the left of the condensers current is fed over windings of the impulse relay A. This circuit includes reversing contacts (Z1 and d2 of relay D. I I

When aconnection has been completely set up and the oalledsubscriber lifts his re-' ceiver to reply to the call, the answering supervisory relay D operates in known manner to reversevfor supervisory purposes by means of its contacts all and d2 the current fiowingin the incoming wires. When these contacts change over, the current in the windings of relay A is reversed as well as the cu r-, rent in the line wires, and owing .to the im-, pedance of the windings of the impulse relay the current reversal takes place more slowly than it would if the current in the relay continued to flow in the same direction as be.- fore with the result that the intensity of the clicks usually heard in a telephone instru-. ment connected to the line is considerably reduced. In order that the clicks may be still further reduced in intensity a condenser in British Specification No. 271,142 previously referred to.

Figure 2 shows an embodiment of the invention applied to a final selector of the type shown in the above specification. The answering supervisory relay D is connected as before. WVhile the switch is being set relay A is connected over back contact all of relay D and back contact h of the selector test or switching relay. If the called line be found free the test relay operates and contact it changes over. The circuit over the right hand winding of relay A now includes front contact h and back contact (Z2. When relay D operates the current in the incoming wires and in the impulse relay is reversed by the operation of contacts all and d2.

Should the called subscribers line be found engaged by the'final selector, the test or switching reh y is not operated but relay D is operated intermittently. During the periods when relay-D is operated, battery is then connected to bothof the incoming wires over front Contact (Z1 and the left hand winding of relay A to one wire and over back contact h of the unoperated test relay and the right hand winding of relay A to the other wire for the transmission of the equipotential lamp flash signal. Contact 062 changes over but has no effect as the circuit over it is open at'contact h.

Contacts all and d2 are shown in Fig. 1 as make-before-break contacts, consequently guarding resistances must be'included in the battery circuit to prevent the short-circuiting of the battery at the momentthe three springs of each contact set are in contact. In Fig. l the resistance is shown included in the impulsing circuit but the contact arrangement shown in Fig. 2 in which ordinary change over contacts are employed, enables the resistance to be omitted from this circuit but yet to be included in the battery circuits when current reversal takes place. The resistances then serve to guard against short circuiting the battery should the three contacts of (Z1 or 0Z2 come together by accident.

WVhat I claim as new and desire to secure by Letters Patent is 1. At a feeding bridge in a telephone system at which a reversal of current in the line wires on one side of the bridge is effected for the transmission of a signal, an impedance connected between the said line wires and the point at which the current reversal is effected.

2. At a feeding bridge in an automatic telephone system at which a reversal of current in the line wires on one side of .the'bridge is effected for the transmission of a signal and in which current isfed to the said wires over the windings of an impulse receiving relay,

connections such that the impulse receiving relay is included in the circuit between the relay, and contacts on said supervisory relay for reversing the connections between said battery and said battery feed relay.

5. In a telephone system, a line having two sections coupled by condensers, a first and a second battery feed relay bridged across said two sections, respectively, in series with a battery, and contacts on said second relay for reversing the current flow in said first-section,

said contacts being located in the circuit be- 7 tween said battery and said first relay.

6. In a telephone system, a line, a doublewound battery feed relay bridged across said line in series witha battery, and means for reversing the current flow in said line, said means including reversing contacts between said battery and said relay.

7. In a telephone system, a line, a doublewound battery feed relay bridged across said line in series with a battery, means for reversing the current flow in said line, said means including reversing contacts between said battery and said relay, and resistances arranged to be included in the circuit between said battery and said reversing contacts only after said reversal has been completed.

8. In a reverse battery signalling system, a line, abattery connected to said line, reversing contacts between said battery and said line, an impedance connected between said line and said reversing contacts so that the current through said impedance is reversed each time said contacts are operated, thereby preventing sudden reversals of current in said line, and a resistance connected between said battery and said reversing contacts to prevent short-circuitingof the battery during reversal.

9. In a telephone system in which supervisory signals are transmitted to a calling line by reversing the current in such line, a battery, reversing contacts for reversing the connections of said battery to said line, and an impedance connected between said line and said reversing contacts to prevent clicks in the telephone on the calling line by decreasing the rate at which the current in the line dies dowfi 

